Vacuum tube circuits



Jan. 14, 1930.

. s. E. ANDERSON VACUUM TUBE CIRCUITS v Original Filed 1500.24. 1925 2Sheets-Shegi i s; E. ANDERSON 1,743,701

VACUUM TUBE CIRCUITS Originalfiled Dec. 24, 1923 2 Sheets-Sheet -2 I v IR$ v Ware Lengm Ware Leny fl? F/ a 7 Wye/770K d/d/veyf Andaman PatentedJan. .14, 1930' ITB STATES sInnnY E. mnnason, or mmwbas,nnwlmnsnmassrenon 'ro wmm' nno'rmc courm, mconrozwrnn, or new YORK, n.r, A conronarron or roan f waves. .The invention has special applicaformof' inter-stage coupling-between the vacuum zrunn "orncurrs aunt-emuuse: was, 24,1a'aasem1 mesaua Renew ed men 16, me.

The present -'inv entionrelates tewave rece'ption, and particularly'tothe reception.

of high frequency waves, [such as radio tion to radio frequencyamplifiers. 1

It is an ob'ect of the'jnvention to secure uniform and igh amplificationover a wide range of wave lengths in the'relatively short wavelengthregion; I I g A rad'o receiving circuit is disclosed in application,Serial No. 654,990 of Dana A.

Griffin, 'filed' August 1, 1923, in which the.

first stage of the radio frequency amplifier comprises two vacuum tubesconnected in push-pull of parallel-opposed relation with respect to theincoming circuit andin which subsequent stages each comprises asinglevacuum tube amplifier. Amongthe advantages of this type of circuit arethat the singing tendency is reduced and'that the wave length range overwhich substantially uniform amplification is obtained a is iconsiderablyj increased over the case where a single tube isused in eachstage. This latter effect is secured by providi'n individual couplings,such as transformers, etween the respective tubes of the push-pullcircuit and the succeeding stage and'by designing these transformers sothat-they have different and overlapping fre uency transmissioncharacteristics. Furt er, when the circuit" is provided with connectionsfor enabling the tubes to serve both. as radio or audiofre quencyamplifiers, after the manner of the so-called reflex] circuit, the firststage of the radio frequency am lifier may advantageouslybe used as thenal stage for the audio pus -pu11 connection, the circuit iscapable ofcarrying a large audio frequency load without impairing the quality.

A more specific ob'ect of vention is to provi e an improved radioreceiving circuit of the general type dis: closed in the Griflinapplication referred A feature of the invention comprises circuitprovisions for enabling the advantages pointed out above in connectionwith the circuit of Grifiins application to be realized in a radioreceiver in which the filaments freqhency amplificatiomand'by virtue ofthe the present in p initial or push-pull stage and-the succeeding thislatter feature comprises a ng transformer and a particular manner ofconnecting the windings of this transformer in the circuit to secure themost eflicient results in accordance with appli 'cants discoveryr. I

An incidental feature comprises the man stages to secure a more uniformtransmission 'throu bout a wide wave, length I range. Speci callthree-wind i ner of connectin --the wave' intercepting circuit withtheinitial amplifier-stage.

' The exact nature of the invention and the variousobjects vand featureswill appear more fully from the following detailed'description of theinvention as embodied in typical radio receiving circuits shown in thedrawing.

Fig. 1 is a schematic circuit diagram of a radio receivin'g circuitof'one form which the invention may take; Fig.11A'sh0Ws a type of loopantenna suitable foru'se with t e invention; Fig. 2 isa'schematiccircuit diagram of'a radio receiver, in which provision ismade fonemployi'ng' the same tubes r'an ement which ma fbeadopted' forthe initial sta e of the Ta '0 frequency amplifier and the amplifier;Figs. 4. and 5 illustrate-.di erent mo es of cOnnection 'of thetransformer windingsbetween-the 'ush-pull stage and the-succeedingstage; ig. '6 is a wow in which may be coupled, preferably variably,

with the secondary inductances 12 and '13. 1

for radio and'audio' frequency amplification after themanner oftheso-cal'led reflex cirsectionofone formwhich the threewindingsinter-stage transformer may take; and Fig. 7 shows curves illustrativeof the effects of ing condenserand with the inductance 11, f

B5\ nal stage of the audio fre uency \Vh'en the switches 14 and 15 areclosed, the secondary tunin condenser 15' is connected across the seconaries 12 and 13, these having interposed between them the fixedcondensers 16, which are prefarbly of large enough capacity not toinfluence the tuning of the secondary circuit to any great extent.

The outer terminals of the secondaries 12 and 13 are connectedto therids of the respective vacuum tubes 17 "an 18, which may be of the wellknown three-element type including a cathode, an anode and a suitabletype of control element, such as the amplifier 22. For the v sake ofsimplicity, however, only one such succeedi'ngstage is shown, this beingcoupled to the detector23 by means of a second radio frequencytransformer 24. The detector 23 isprovided with the usual grid leakandcondenser arrangement shown, and includes in itsoutput circuit areceiver R of any suitable-type, such as a head set or a loudspeakingreceiver- Space current is supplied to all of the tubes from the commonsource 28.

The filamentary cathodes of all of the tubes are connected in serieswith each other and the filamentheating source 25, the negative pole ofwhich is connected to earth. This heating circuit may be traced from thegrounded pole of battery 25, first through the filament, of the detector23, then through the filament of the second stage amplifier 22, thenthrough the filament of the tube 17, and finally through the filament ofthe tube 18 to the positive pole of the battery In order thatthe tubes17 and 18 may operate properlyin a balanced amplifier circuit, it isnecessary that the grid of each tube have the proper normalpotentialrelations with its own filament, and ingeneral, the samepotential with respect to its filament. .The I proper grid polarizationfor these tubes is obtainedin accordance with the invention byconnectingthe grids to the proper points in the series filament heatingcircuit. For example, 1t' Wlll be seen'that the grid of the tube 17isc'onnected' to the more negative terminal of the filament of tube 22.which filament is, included in the series filament heating-circuit, nexttothe filament of the tube. 17in the direction of the negative pole. ofthe filament heating Ii d." These tubes 17 and 18 are connecte inparallel-opposed or push-pull relation. with respect to the incomingcircuit 10, 11' and battery. The grid of the tube 17 is. thereforepolarized more negative than the negative end of its cathode by theamount of potential drop in the filament of tube 22.-

Similarly, the grid of the tube 18 is connected to the more negative endof the filament of tube 17, which filament is included between thenegative pole of battery 25 and the filament-of tube 18 and is nextadjacent the filament of tube 18 in the filament heating circuit. Thegrid of the tube 18 therefore possesses a polarizing potential which ismore negative than the negative end of its ,own filament by the amountof the potential drop through the filament of the tube 17. Since tubesmay readily be selected which have substantially the same filamentresistance, the polarization of the grids of tubes 17 and 18 ma by thecircuitarrangement just-describe be made for all practical purposes eual. I

The grid 0 the amplifier 22 may. in a similar manner be polarized morenegatively than its own filament by connecting it, as shown, to the morenegative end of the filament of tube23. 1

This mode of connection of the filaments in series is of particularadvantage in the 7 case of tubes using low voltage filaments,

such as the well known dry cell tubes. Such tubes require only smallenergy to heatv the filaments. ,It is advantageous to connect theirfilaments in series's nce dry.

therefore be made from the common filament circuit of these tubes to themid-point of the secondary of the input transformer. When the seriesfilament heating circuit is :employed, however, independent conductivecircuits must be maintained between each grid and a different point ofthe filament heating circuit so that a different mode of impressing thewaves on the grids must be adopted. In

accordance with the invention, individual alternating current paths areprovided from each grid through one or the other of the secondaryinductances 12 or 13 and one or the other of -the condensers 16 to acommon point in the; circuit, such as ground. Since the cathodes are.also connected to ground.

the alternating current potentials im ressed on the two grids may hemadeequal y this form of connection. I

In' order to make use ofthe push-pull cir-.

cuit to secure a broader characteristicvfor the amplifier, it isnecessary, as pointed out above, to provide transmission paths betweenthe individualtubes 17 and 18 and the sec- 0nd stage tube 22, whichpaths have respecinsome cases the use of two separate transformersintroduce difficulties, the causes of which are not thoroughlyunderstood',-but which may be due to different phase relations existingbetween'the waves in the two transformers so that in one region of'thewavelength range a different res'ultantefi'ect is obtained from thatwhich exists in adifferent region of the wave length range. Suchdifficulties have been overcome in accordancewith the inventionbyproviding a threewinding transformer comprising the primary windings 19and 20 and the common secondary winding 21. I

The manner of constructin'g this trans- These grooves have relativelygreat depth compared with their width. In one instance,

the spool had an external diameter of the order of 2 inchesfeach groovewas of the order of inch deep and of 5 ofian inch, or preferably less,in width. No attempt has been made in Fig. 6 to employ a scale to denotethe preferred relative dimensions.

In Fig; 6, the preferred positions of the windings 19, 20 and 21 areindicated. "The spacing between the respective windings and thenumber ofturns in each winding' may be varied depending on the wave lengths to betransmitted, the design of the tube used, etc.,

and in general it will be found that'by using a different number ofturns in the two windings l9 and 20 and by properly relating thesewindings to the common secondary 21, the amplifier will be given a muchbroader wave length characteristic than as though the windings 19 and 20had each the same number of turns. The proper number of turns to be usedin an initial case may be determined by a cut-and -try method, and itwill in general be readily observed whether a given change inthe'number' of turns improves the characteristic in the desireddirection or not, so that by a few successive tries, with the previousknowledge that the number of turns in the windings 1 9 and 20nectionis'sliownin Figs. 4, 5 and 7. In-Fig.

4, the anode ofthe'tube 17 is connected to the outerterminal of thewinding 19, this terminal being indicatedin- Figs. 4 and 6 as o. Theanode of the tube 18 is connected to the inner ter'minalof the winding20, this being indicated in-Figs. 4 and 6 by i. The

other terminals'of the windings 19 and 20 are connected together andthrough the plate battery to the filament circuit. The inner terminalofv the-winding 21' is connected to the grid of the tube 22 and theouter termi nalis connected to the filament circuit. With this type ofconnection it is found that a characteristic of relatively narrow wavelength range and with the highest amplification at the'central portiononly is obtained.

This is indicatedby the curve I 'of'Fig. 7. It

is, of'course,'immaterial whether the plate of the tube 17 is connectedto the outer termii nal of the'winding 1-9 or whether the plate formeris best illustrated in Fig. 6 to which reference will now be made.The'spo'ol 26, preferabl of insulating material, has cut into it t reeparallel, concentric, annular grooves, in which the windings are placed,

of the tube 18 is connected to the outer terminal of the, winding20solong as the plates of' the respective tubes are "connected torespectively opposite terminals, that is, one to theouter and theother'to the inner. It isalso immaterial whether the grid of thetube'22'is' connected to the inner or the outer I terminal. So long asthe plates of the tubes 17"a-nd' 18 are connected to respectively op- 1primary windings,however, as in Fig. 5, so

that the anodes of both tubes 17 and 18316 connected to the analogousterminals of the windings 19 and 20, a broad characteristic,

such as is shown by the curve II'of Fig. 7, is obtained. No explanationof this effect is attempted here except that it is probably due to thecapacity relations between the different windin s, it being known thatat the relatively s ort wave lengths the capacity "effects betweendifferent portions of the cir-' cuit have considerable influence on thetransmission characteristics.

- In reversing the terminal connections of a winding in this manner, itis of course necessary that the direction of the winding itself be alsoreversed to avoid the output of one of the tubes 17 opposing that of theother tube 111 its effect in transmitting waves to the commonsecondary.i

The transformer 24 preferably has a wavelength gaincharactenstic suchthat it cooperates with the transformer 19, 20, 21 to give substantiallyuniform transmission over, a

"wave-length range as broad as the characteris'tic of the transformer19, 20, 2 1 alone.

This may resu1t, for example, from the transformer 24 having its highestin displaced in the wave-length range mm the point or points of highestgain of amplifier 19, 20, 21 so that the combined effect of the twotransformers in giving uniform transmission is superior to either alone.

.The circuit of Fi l employs an open antenna 10, 11. If itlie desired touse a 100 antenna, the switches 14 and 15 are open and the double loopshown in Fig. 1A is connected to the receiving circuit at the terminalsa, b, c and J, respectively. With this manner of connection. theindividual inductances Hand 13 are replaced in the circuit bytheindividual loops.

Fig. 2 illustrates a. circuit of the same general type as that showninFig. 1, the

,main difference being that in Fig.2 additional elements are providedfor enabling the radio frequency amplifier tubes to serve also for audiofrequency amplification. This is accomplished by includingin theoutput-of-the detector tube 23, the primary of an audio frequencytransformer, the secondary of which is included in the grid-cir-' cuitof the tube 22 so that the detected audio frequency waves are impressedu on the tube .22 for amplification. The amplified audio frequency wavesfrom the tube 22 pass into the primarywindings of the audio fre- .quencytransformer 31, the secondaries of whichaPe included in the respectivegrid Themanand 18 .serve as a balance or. push-pull amplifier' for theaudio frequencywaves, the

amplified waves ap aring inthe primary of the output trans ormer 32leadin to the receiver R of any suitable type. T e various audiofrequency transformers are preferably provided with small radiofrequency by-pass condensers in accordance with the usual practice.

A somewhat simplified alternative type of connection is shown in Fig. 3.This figure shows only so much of a radio receiving cir-- cuit as liesto the left .of the broken line BB of Fi 2, it being assumed that theportion of 2 lying to the right of this line is tobe added to thecircuit of Fig. 3 to the right of the .line B--Bf. In the modifiedcircuit arrangement of Fig. 3, the

filaments of the tubes 17' and 18 are connected in parallel with eachother, and this ary of' the audio frequency transformer 31' is includedserially 1n the common branch of the tubes 17' aand 18, it beingrememberedthat the conductor 5 of Fig. 3 corresponds to the conductor 5of Fig. 2 and leads The mode of operation of each of the types ofcircuit that has been describedwill be apparent from the detaileddescription of the circuits already 'ven, and in general will be thesame for eac of the types shown,

except that in the case of Fig.3, as pointed out above, the tubes 17'and 18 are connected in' parallel for the audio waves and not ,in'parallel-opposedor push-pull relation as n the other figures.

articular wave length region nor to anyo the values or dimensions thathave been given, nor to the Epecific circuit arrangements that have beenescribed and shown in detail, but only by the scope of the appendedclaims.

'What is claimed 1s: I I

1. In a radio receiver, inductance compris- .ing 'two separate coils,two vacuum tubes each having a 'd or im edance control It is to beunderstood that the invention vis not to be limited to any element,anano e 'and'a' cat ode, said .cathodes being in series with each otherand with an external heating source; one terminal of each "of saidcoilsbein connected to a different re ective grid, t e other terminalsof said coils having individual connections to the cathodes of, saidtubes, acapacity for,

reasonating with said two-coil inductance at the frequency of the wavesto be received,

and a receiv ng instrument associated with said anodes.

2. In a radio recelver two wave-intercepting loops, two-vacuum tubeseachhaving a cathode, an anode, and a gridor impedance control element,one terminal of eachloop being connected. to a different respectivegrid, connections from the other terminals of said s to earth and tosaid cathodes,'a ca ,acity or resonating with said,

two loops an a receiving instrument operatively associated with saidcathodes and anodes. e

3. In a repeating circuit, incoming and outgoing circuits, a repeaterstage comprising two vacuum tubes, connected in arallelopposed relationwith respect to sai incomin and outgoing circuits, a third vacuum tu econnected between saidstage and the outgoing circuit, each ofsaid tubeshaving a cathode ada ted to be heated, and a grid, and an ano e, asource of cathode-heating current, said cathodes being connected 'inparallel-opposed relation with respect to said incoming circuit, eachtube having a cathode,

an anode and .a grid, said grids being con nected to the. respectivefree terminals of said inductance portions and separate gridpolarizingconnections irom the respective,

terminals of said capacity to the respective cathodes of said vacuumtubes.

5. In a radio receiver, an amplifier stage I comprising a pa1r of vacuumtubes com ected in balanced relation, another stage working] th rs entin tandem with the first-mentioned stage comprising said tubes cathodesbeing connected in series with one another and with said source, andconnec-- tions from each of the grids of said balanced 'p tubes to suchpoints in the cathode-heating circuit that both of said grids have thesame normal potential with respect to their respective cathodes.

6. In a radio receiver, a wave intercepting circuit, a radio-frequencyamplifying stage associated therewith comprising a pair of vacuum tubeseach having a cathode, an anode, and a grid, said tubes being connectein balanced relation with respect to the wave-intercepting circuit, anindividual inductive winding connected between the cathode and anode ofeach tube, a second amplifying stage comprising a single vacuum tubehaving an input winding inductively coupled to said two windings, saidtwo windings having a different number of turns causing un-. equalcoupling with the third winding and establishing two wave repeatingpaths having substantially difierent transmission characteristics toenable the transmission of a wider wave-length range than is efiectivelytransbetween either of the said pair .of

mitted tubes alone and the third tube.

7. In an amplifying circuit,- anincoming:

circuit, an outgoing circuit, receiving means associated tween sailncoming and outgoing circuits, each of said tubes having a cathode,ananode and a grid element, said incoming circuit densers, a connectionfrom a point in said ial 'yvo'ii tn iarm d; me cathode-and- -gnd asingle vacuum tube, each of having a cathode adaptedto be heated, and agrid, a source of current, the

'pote'ntia sto the grids ofgjsaid reference to theirrespective-'cathodm'said means comprising connections from." said 7grids to difierent points on sa'id series circuit.

13. A vacuum' 'tube'circuit comprising -a v and fa? source, otener withsaid outgoing circuit, a air of electron discharge tubes connect inparallel-o posed relation with each other be potential drop incomingcircuit between said condensers to the cathodes of said tubes, aconnection'from the other terminal'of each inductance to a respectivegrid, individual grid-polarizing conductive connections from therespective grids to the cathodes of said tubes, and a tunin'con'denser'connected across said grids.

8. n a radio receiving system, asource of waves," an amplifier for saidwaves including a plurality of space discharge tubes havingrespectlvecontrol electrodes, cathodes and anodes, said-cathodes beinconnected in a series circuit to asource 0 heating current,inputcircuits for a plurality ofsaid tubes, including "alternatmgcurrent paths connected'to the same point on ,sa d' serles c rcuit, anddlrect' currentcon- 'duct ve paths connected tofdifierent points i9. A--'vacuum tube: circuit.- "comprising a i a p h'p a v iand'meansforapplymgto the g d er-pna ,of-said' tubes ,drop across the cathode ofanfsai fijtfibes other 1 p -pullrelation, each aving -citthode. and grm-"said cathodesvac il ifin elircui ip f s being-connected inseries,iandmeans fo'rja lying" to the gridiiofione "of said tubes t eP)tential p @1955 vthe thodeof another v of said tubes. I 11. A vacuumtube circuit comprising a plurality of tubes in ushull'arrangement, eachhavinga catho e an grid, said oath odes being connected in series with asource of energy, means for applying to the grid of one of said tubesthe potential drop across 6. the cathode ofanother of said tubes, and

means for causing thefgrids of said tubes to have the same biasingpotential with reference to their respective cathodes.

12. A vacuum tube circuit comprising a plurality of tubes in ushullarrangement, each having a catho e an odes being serially connecte withasou'rce of ener means for applying-equal-biasing' airoftubesinf'ush-pull arrangementeach ay ng;.a';cath e' and grid, said cathodes bemgser ally connected with a resistance plying t'o thegrid 0 one of saidtubes t e through the cathode of the rid of said ing serially'jconnectedwith a resistance and other, tube, the potential drop t rough said andmeans for a tubes --wit I tube circuit comprising a the voltage dropthrough said serles circuit a source of energy, and means for applyinequal biasing potentials to the grids of sai vacuum tubes with referenceto their respective cathodes, said means comprising connections for applthrough the catho e of one of said tubes to the grid of the other, andthe potential drop through said resistance to the grid of said firsttube. p a

15. A vacuum tube circuit comprising a air of tubes in pushullarrangements, each aving a cathode an grid, saidcathodes bee ingserially connect-ed-inta circuit having at least one resistanceelement-and a source of energy, and means for applying a portion of tosaid grid electrodes to tentials therefor.

16. A vacuum tube circuit plurality of tubes in obtain biasing pohavinga plurality of resistances, and a source of energy, and means forapplying thev voltage drop through different portions of said vseriescircuit to said rid electrodes to obtain biasing potentials t erefor.

In witness whereof, I hereunto subscribe 'my name this 17 day ofDecember A. D.,

SIDNEY E. ANDERSON.

ing the potential drop 1 comprising a ush-pull arrangement, 7 :eachhaving a catho e and grid, said cathodes being serially connected in acircuit

